1. Technical Field
The present invention relates to integrated circuit devices that drive electro-optical panels such as an EPD (electrophoretic display) panel. Furthermore, the invention relates to electronic devices equipped with such integrated circuit devices together with electro-optical panels.
2. Related Art
Display devices that use EPD panels or the like and are also called electronic papers have been developed as display devices that achieve a further reduction in thickness and power consumption compared with liquid crystal display devices, plasma display devices, and the like, and are used in electronic devices such as wrist watches, electronic books, electronic newspapers, electronic advertisement boards, and guide display boards.
For example, in an EPD panel, an electrophoretic layer is arranged between a transparent top plane electrode provided in a surface layer and a plurality of segment electrodes provided in a lower layer. The electrophoretic layer includes microcapsules each containing white electrophoretic particles and black electrophoretic particles that are charged to have different polarities, and a dispersing medium (transparent oil etc.) for dispersing these electrophoretic particles.
By applying a voltage between the top plane electrode and the segment electrodes to apply an electric field to the electrophoretic particles, the electrophoretic particles move in accordance with the direction of the electric field, and colors of pixels corresponding to the segment electrodes are displayed. The EPD panel is nonvolatile (i.e., has a memory function). That is to say, when the electric field is applied to the electrophoretic particles once to achieve a display state, the EPD panel maintains this display state even if the electric field is thereafter not applied to the electrophoretic particles.
Accordingly, a driving voltage need only be applied to the EPD panel only when performing initial display and when changing or erasing the displayed content, and therefore, significant power-saving can be achieved. However, when changing the driving voltage, the power is necessary for driving capacitance components between the top plane electrode and the segment electrodes. In addition, since resistance components exist between the top plane electrode and the segment electrodes, a leakage current flows and power is consumed also in a time period in which a DC voltage is applied to the EPD panel.
As a related technique, JP-A-2009-237029 (paragraphs 0007-0008 and FIGS. 1 and 3) discloses that, in a display device which continues to display an image even if a display element is not driven, the time taken until the image is displayed is shortened and the power consumption in a driving device is reduced. This driving device includes a voltage boosting means for boosting the voltage of a power supply, a driving means for driving a display element group, a switch that turns on or off with a first end thereof connected to the voltage boosting means and a second end thereof connected to the driving means, and a control means for causing the switch to turn on from an off state while continuing to cause the voltage boosting means to boost the voltage to cause the driving means to drive the display element group with the boosted voltage, and switching the state of the switch so as to turn off from an on state after the driving ends.
According to JP-A-2009-237029, it is possible to reduce the power consumption after a driving period in which the driving means drives the display element group ends, by turning on the switch in the driving period and then turning off the switch after the driving period ends. However, JP-A-2009-237029 does not disclose a reduction in the power consumption in the driving period.